The present invention relates to a sampling valve for aspirating and pushing a liquid specimen such as blood in cylindrical shape, and sampling quantitatively, and more particularly to a sampling valve for sampling by selecting only a portion of the sample necessary for measurement.
An apparatus for counting blood corpuscles such as erythrocytes, an apparatus for classifying leukocytes, and an apparatus for counting reticulocytes are well known. An apparatus which combines these plural functions into one (multifunctional apparatus) is also known. The multifunctional apparatus is capable of obtaining measuring results of multiple items by one sampling operation. Depending on the specimen, however, unnecessary items are also measured, and the samples and reagents are spent wastefully.
To eliminate such waste, a function for sampling and taking into the apparatus to analyze (discrete test function) only a necessary sample for each specimen is required. For example, in the field of biochemical examination, the sampling method includes aspirating a necessary amount of sample from a pipette, and discharging the sample into a reaction vessel. This method requires a simple structure, but precision is poor. In particular, it is a problem when handling a highly viscous sample such as blood. Accordingly, in the blood cell counting apparatus, the specimen is sampled by aspirating and pushing the specimen in cylindrical shape by means of a sampling valve, and quantitative removal.
Referring now to FIG. 1 and FIG. 2, the structure and operation of a general sampling valve are briefly described below. Usually, a sampling valve consists of two fixed elements 10, 14 and a movable element 12 enclosed by the fixed elements 10, 14. FIG. 1 and FIG. 2 show two states of the sampling valve. In FIG. 1, the specimen flows in the direction of arrow A, that is, from a pipette 16 to a flow-in passage Q, metering (measuring quantity) passage P1, and flow-out passage R1, and fills up the metering passage P1 of the movable element 12 (which is called the first state). As the movable element 12 moves from the first state, it comes to the state in FIG. 2 (which is called a second state), and the specimen in the metering passage P1 in the first state is pushed out, and is transferred outside the sampling valve, together with a liquid such as a diluent in the direction of arrow B from the passage T2 to the passage T1.
In the apparatus for sampling a specimen by means of a sampling valve, there has been a keen desire for a sampling valve applicable to a discrete test in order to realize such discrete test as mentioned above (for sampling only a necessary portion in each specimen and analyzing).